Non-circular chromosomes require a specialized mechanism for maintaining chromosome ends after each cell division because the polymerases responsible for replication of chromosomal DNA are unable to fully replicate linear DNA molecules, creating an “end replicating problem.” To meet this challenge, eukaryotic cells depend upon an enzyme, telomerase, to add short, typically G-rich, relatively conserved repeats onto chromosomal ends. These repeat structures are termed telomeres.
The presence of telomeres is essential for cell viability. The absence of even a single telomere leads to cell cycle arrest in yeast, a eukaryotic cell (Sandell and Zakian, Cell 75:729, 1993). Telomeres shorten during replication; telomerase restores the telomeres. Thus, as expected, telomerase activity is primarily detected in actively dividing cells. As such, telomerase activity is constitutive in unicellular organisms and is regulated in more complex organisms, relatively abundant in germline and embryonic tissues and cells as well as tumor cells. In contrast, telomerase activity is difficult to detect in normal somatic human tissues. Moreover, rather than cessation of replication resulting in decreased telomerase, recent data indicate that telomerase inhibition might be one of the critical events in this transition. The seemingly direct correlation of telomerase/replication activities have prompted much speculation that inhibitors of telomerase could be a “universal” cancer therapeutic, effective for essentially all tumor types, whereas stimulators of telomerase could overcome the observed natural senescence of normal cells.
Spurred by these models, characterization of telomerase for culmination in isolation and cloning of telomerase has been a high priority. The mechanism of telomere elongation has been shown to center on the G-rich strand of the telomeric repeats. This G-rich strand, which extends to the 3′ end of the chromosome, is extended by telomerase, a ribonucleoprotein, from the RNA component, which acts as a template. Various components of this complex have been isolated and cloned. The RNA component of the complex has been isolated and cloned from many different organisms, including humans (Feng et al. Science 269: 1236, 1995), mice and other mammalian species, Saccharomyces cerevisiae, Tetrahymena, Euplotes, and Oxytricha (see, Singer and Gottschling, Science, 266: 404, 1994; Lingner et al. Genes & Develop. 8: 1984, 1994; and Romero and Blackburn, Cell 67: 343, 1994). Protein components have been relatively refractory to isolation. Recently, the nucleotide sequences of several protein components have been determined (an 80 kD/95 kD dimeric protein from Tetrahymena, WO 96/19580; and a 67 kD protein from humans, WO 97/08314).
The present invention discloses nucleotide and amino acid sequences of telomerase, uses of these sequences for diagnostics and therapeutic uses, and further provides other related advantages.